The present invention relates to a printer which prints data at high speed through use of a multi-head having a plurality of printing heads placed thereon, wherein the printing heads form a plurality of printing elements. More particularly, the present invention relates to an ink-jet printer, a laser printer, an LED printer, or a thermal recording printer.
The dominant existing printer for recording a color image is an inexpensive color printer having a simple structure. In order to enable a common ink-jet serial printer such as that shown in FIG. 4 to print a high-quality monochrome or color image at high speed, the resolution of nozzles must be increased by increasing the density of nozzles of a printing element 101, the element recording an image on recording paper 102 wrapped around a platen 103, as well as to increase the printing speed of the printing element 101 by increasing its length in the secondary scanning direction and increasing the number of nozzles. As a result of a reduction in the particle weight of a droplet to be squirted from the nozzle and an increase in the number of nozzles, an inexpensive ink-jet printer having a resolution of about 720 dpi has recently been realized.
However, a further increase in the density of printing elements involves an increase in the precision of a mechanism including the printing elements, thus adding to the cost. To prevent an increase in the cost, there is employed an interlaced driving method which uses a plurality of comb-shaped heads arranged in the primary scanning direction and offset from one another in the secondary scanning direction.
FIG. 5 shows nozzles of a conventional interlaced printing apparatus. Reference numeral 301 designates a nozzle for squirting recording ink (hereinafter may be referred to simply as "ink"); 302 to 305 designate ink squirting elements; 307 designates a retaining section; and 308 designates printing signal cables and ink feed pipes. The plurality of nozzles 301 are arranged in a line at given intervals, and one head is wholly formed from a plurality of nozzle lines. At the time of a primary scanning operation, data corresponding to print positions are supplied to the squirting elements 302 by way of the cables 308, so that ink is squirted from the nozzles 301 to thus record the data on the paper.
However, in the conventional interlaced printing apparatus, the number (N) of nozzles 301 constituting a multi-nozzle is 15, and the nozzles 301 are formed at a pitch (K) of 4 or so. Accordingly, the resolution of the nozzles is 720 dpi or less. If an attempt is made to increase the density of printing elements in order to increase resolution to 1000 dpi or more, which allows printing of halftone dots, the apparatus suffers a problem of a drop in print speed.
If an attempt is made to increase the print speed by increasing the number of nozzles, manufacturing yields of a print head are deteriorated, adding to cost.